Thermal motor protector with gas producing arc chamber



y 1965 H. F. MALONE 3,183,326

THERMAL MOTOR PROTECTOR WITH GAS PRODUCING ARC CHAMBER Filed Dec. 14, 1962 INVENTOR. Heme! 72 Maze/1e.

United States Patent 3,183,326 THERMAL MOTOR PROTECTOR WITH GAS PRODUCING ARC CHAMBER Homer F. Malone, Jackson, Mich, assignor, by mesne assignments, to Mechanical Products, Inc., Jackson,

Mich., a corporation of Delaware Filed Dec. 14, 1962, Ser. No. 244,776 3 Claims. (Cl. 200-120) This invention relates to an improved motor protector.

Motor protectors are often incorporated into the field winding sub-assembly of an electric motor prior to the application of a protective coating thereto. Such a coating, for example, a varnish, seals the windings against moisture, dust and deleterious environmental conditions.

However, in order for a motor protector to be placed in such integrated association with a sub-assembly of an electric motor, it is necessary that the motor protector be a completely self-contained unit capable of consistent performance throughout the life of the motor.

Motor protectors heretofore known and used fall somewhat short of meeting this requirement, since the problem of minimizing the detrimental efiects of arcs drawn between the contacts when they open has not been solved in a manner that gives the motor protector an expected life equivalent to that of the motor itself. In such known motor protectors, the engaging surfaces of the separable contacts often become pitted and burned, changing the resistivity of the motor protector and ultimately leading to failure thereof.

An improved motor protector in accordance with the instant invention overcomes the problem of the pitting and burning of the engaging surfaces of the separable contacts by enveloping the contacts entirely within a gasproducing chamber. The gas produced in the presence of an arc has a cooling and quenching effect on the are.

In accordance with the instant invention, the arc chamher is of hollow hexahedron construction, one side of which is open for the acceptance of a pair of separable contacts. The chamber is constructed as by induction molding a composition comprising alumina tri-hydroxide with approximately 15% glass reinforcing material sold under the trade name Rosite. This material has the particular characteristic that when it is exposed to an are, it emits a gas containing CO and Water, which has a cooling and quenching efiect on the arc. In addition, the increased gas pressure tends to blow and stretch the arc toward the open end of the arc chamber.

The are chamber is constructed so as to interlock with a contact-carrying heater to positively position and retain the heater and contact.

Accordingly, one object of the instant invention is an improved motor protector.

Another object is a motor protector having an arc chamber that cools and quenches an electric arc.

Another object of the instant invention is a motor protector having an arc chamber which envelops the separable contacts thereof.

Another object of the instant invention is a motor protector having an arc chamber that is interlocked with a heating element.

Another object of the instant invention is a motor protector having an arc chamber which acts as an insulating medium between the pair of separable contacts and the motor protector housing.

Other objects and advantages of the instant invention will become apparent from the following description, claims and drawings, wherein:

FIGURE 1 is a top view of a motor protector in accordance with the instant invention, partially broken away to show the interior thereof;

3383,3226 Patented May ll, 1965 FIG. 2 is a cross sectional view taken substantially along the line 2-2 of FIGURE 1; and

FIG. 3 is a perspective View of the arc chamber utilized in the motor protector of the instant invention.

A motor protector 10, in accordance with an exemplary constructed embodiment of the instant invention, comprises a steel housing 1.2, of generally tubular construction having an open end 14 for the acceptance of the electrically energized components of the motor protector 10.

An arc chamber 16 molded from, for example, Rosite, is disposed internally of the motor protector housing 12. The are chamber 16 is retained within the housing 12 as by a press fit, an open side 18 thereof facing the open end 14 of the motor protector housing 12.

The are chamber 16 is relatively long so as to extend well into the housing 12, thereby to preclude arc transfer to the metallic housing 12.

A heater element 29, having a generally step-like vertical cross section, extends longitudinally within the motor protector housing 12, an inner end portion 22 thereof supporting a fixed contact 24. A pair of laterally outwardly extending ears 26 and 2.8 on the inner end portion 22 of the heater element 26 are interlockingly engaged in a pair of complementary laterally opposed notches 30 and 32 in the arc chamber 16. The notches 30 and 32 in the arc chamber 16 serve to position and retain the inner end portion 22 of the heater 20 relative to the housing 12. The arc chamber 16 has a second pair of notches, one of which is shown and designated by the numeral 34, adjacent the top thereof to expedite assembly of the motor protector by eliminating any requirement for specific orientation of the arc chamber 16 relative to the housing 12.

The heater element 20 has an aperture 36 in an opposite end portion 30 thereof for the acceptance of a rivet 40 that retains the electrically energized components of the motor protector 10 in the assembled condition. A terminal 41 is electrically connected to the outer end portion 38 of the heater 20.

it should be noted that the central portion of the heater element 20 is of a generally serpentine configuration, the exact shape being dictated by the resistance required in a specific application for the motor protector 10.

A bimetallic snap-acting blade 42 is mounted directly above the heater element 20. The blade 42 has a movable contact 44 secured to an outer end portion 46 thereof, as by welding. The movable contact 44 is aligned and engageable with the fixed contact 24, to complete an electric circuit through the motor protector 10.

The bimetallic blade 42 has a circular aperture 48 therein for the acceptance of a boss 50 on an insulating spacer 52 that electrically isolates the blade 42 from the heater 20. The bimetallic blade 42 normally maintains the movable contact 44 in a closed condition relative to the fixed contact 24, but is responsive to a temperature rise to bias the movable contact 44 to the open condition.

A generally forloshaped blade control member 54 over. lies the bimetallic snap-acting blade 42, end portions 56 and 58 thereof extending to close proximate relationship to the edge of a generally circular nondevelopable surface at? on the bimetallic snap-acting blade 42. The control member 54 assures snap action of the blade 42 at a desired predetermined temperature. The control member has a generally step-like end portion 62 that is electrically connected to a terminal 64. The blade control member 54 has an aperture 65 for the acceptance of the circular boss 50 on the spacer 52. Suitable insulating spacers 66 and 68 are disposed above and below the electrically energized components of the motor protector 10 to insulate them from the metallic housing 12. In addition, suitable insulating spacers '70 and '72, are disposed above the member 54: and below the heater 20, respectively, and retained by the rivet 4d. After assembly of the foregoing components within the housing 1.2, the open end portion 14- thereof is sealed as by epoxy, generally designated by the numeral '74.

A motor protector constructed in accordance with the instant invention is relative well suited for integration with a green winding of an electric motor prior to varnish dipping. Since the motor protector has a relatively long life expectancy, the motor manufacturer or user will not be faced with the problem of replacing a defective motor protector in an otherwise useable electric motor.

The motor protector features a novel arc chamber that is disposed at one end of a metallic housing for the motor protector in such a manner as to insulate the separable contacts and any are drawn therebetween from the metallic housing, as well as to cool, quench and stretch the arc. The are chamber is provided with a plurality of grooves for the acceptance of complementary ears on a heater so as to positively position and retain the heater relative to the interior surface of the arc chamber and motor protector housing. This is particularly important, since the fixed contact is directly supported by the heater.

It is to be understood that the specific construction of the improved motor protector herein disclosed and described is presented for the purpose of explanation and illustration and is not intended to indicate limits of the invention, the scope of which is defined by the following claims.

What is claimed is:

1. A motor protector comprising a housing,

a pair of terminals extending outwardly of said housing,

an elongated heater having opposite end portions mechanically secured against movement relative to said housing, one end of said heater being eletrically con. nected to one of said terminals,

a fixed contact on the other end of said heater,

a bimetallic blade extending generally parallel to and spaced from said heaterhavin-g one end portion electrically connected to the other of said terminals and a free end portion,

a movable contact on the free end portion of said blade engageable with said fixed contact, and

a gas producing arc chamber within said housing of generally hexahedron construction having an open side through which said heater and blade extend, said are chamber substantially enveloping said fixed and movable contacts on five sides thereof.

2. A motor protector comprising a housing,

a pair of terminals extending outwardly of said housing,

an elongated rigid electrically conductive member in said housing having opposite end portions secured against movement relative to said housing,

a fixed contact on one end of said rigid member,

a bimetallic blade extending generally parallel to and spaced from said member having one end portion electrically connected to the other of said terminals a free end portion,

a movable contact on the free end portion of said blade engageable with said fixed contact, and i a gas producing arc chamber within said housing of generally hexahedron construction having an open side through which said blade and member extend, said chamber substantially enveloping said fixed and movable contacts.

3. A motor protector comprisin a metallic housing,

a pair of terminals extending outwardly of said housing,

a heater electrically connected to one of said terminals,

a fixed contact on said heater,

a bimetallic blade extending generally parallel to and spaced from said heater having one end portion electrically connected to the other of said terminals and a free end portion,

a movable contact on the free end portion of said blade engageable with said fixed contact, and

a gas producing are chamber Within said housing of generally hexahedron construction having an open side for the acceptance of and substantially enveloping said fixed and movable contacts to preclude arc transfer between said contacts and said metallic housing, and effect quenching and cooling of said are, said heater having a pair of ears interlockingly engageable with said are chamber to position and retain said heater against movement relative to said housing.

References titted by the Examiner UNITED STATES PATENTS 2,820,870 1/58 Moksu 200-138 2,917,607 12/59 Sterling 200-149 2,994,754 8/61 Nebking 200-122 3,012,122 12/61 Clelland 200-138 3,071,666 1/63 Ellsworth 200-149 BERNARD A. GILHEANY, Primary Examiner. 

1. A MOTOR PROTECTOR COMPRISING A HOUSING, A PAIR OF TERMINALS EXTENDING OUTWARDLY OF SAID HOUSING, AN ELONGATED HEATER HAVING OPPOSITE END PORTIONS MECHANICALLY SECURED AGAINST MOVEMENT RELATIVE TO SAID HOUSING, ONE END OF SAID HEATER BEING ELECTRICALLY CONNECTED TO ONE OF SAID TERMINALS, A FIXED CONTACT ON THE OTHER END OF SAID HEATER, A BIMETALLIC BLADE EXTENDING GENERALLY PARALLEL TO AND SPACED FROM SAID HEATER HAVING ONE END PORTION ELECTRICALLY CONNECTED TO THE OTHER OF SAID TERMINALS AND A FREE END PORTION, A MOVABLE CONTACT ON THE FREE END PORTION OF SAID BLADE ENGAGEABLE WITH SAID FIXED CONTACT, AND A GAS PRODUCING ARC CHAMBER WITHIN SAID HOUSING OF GENERALLY HEXAHEDRON CONSTRUCTION HAVING AN OPEN SIDE THROUGH WHICH SAID HEATER AND BLADE EXTEND, SAID ARC CHAMBER SUBSTANTIALLY ENVELOPING SAID FIXED AND MOVABLE CONTACTS ON FIVE SIDES THEREOF. 